(a) Field of the Invention
The present invention relates to a quadrature demodulator used for a high-speed wireless system. More specifically, the present invention relates to a quadrature demodulator for using recovered signals to detect and compensate for gain and phase imbalances between the in-phase and quadrature-phase components of complex numbers, the gain and phase imbalances being generated from the quadrature demodulator.
(b) Description of the Related Art
A high-speed wireless system receives signals through an antenna, demodulates them through an RF unit and an IF unit, and recovers the signals. Respective units for processing the signals received through the antenna perform a frequency down-converting function and a signal-amplifying function so as to obtain desired signals.
For this, the RF unit and the IF unit use various analog elements including a mixer and an amplifier. The elements satisfy predetermined standards to a certain degree, but the standards have restrictions, and the input signals are deteriorated because of incompleteness of insulation and quadrature between the elements.
The incompleteness of quadrature causing the signal deterioration frequently generates gain and phase imbalances between the I-phase and Q-phase components. The gain and phase imbalances are generated because the respective elements' insulation and signal generation do not provide a complete 90-degree phase between the I phase and the Q phase components, and they deteriorate the demodulator function of a modem for recovering signals. Hence, a method for eliminating the gain and phase imbalances between the I-phase and Q-phase components is required.
So as to remove the gain and phase imbalances between the I-phase and the Q-phase components, several methods using an RF direct conversion receiver are proposed. Among them, the U.S. Pat. No. 6,044,112 entitled “Method and apparatus for correcting amplitude and phase imbalances in demodulators” by Joshua L. Koslov, granted on Mar. 28, 2000, proposes a method for correcting the gain and phase imbalances by using a plurality of complex adders, multipliers, and counters. However, the method by Joshua L. Koslov increases complexity of realization because of using multipliers of complex numbers, and it is sensitive to noise in the case of a demodulator with noise because it is realized using simple counters. Since this method sets the gain and phase imbalances according to an increase/decrease of counts, its response speed is changed according to the increase/decrease width of the counts. The response speed does not reflect the patterns of the actual received signals, but rather it is problematically determined according to increase/decrease intervals of the counts.
Further, U.S. Pat. No. 5,949,821 entitled “Method and apparatus for correcting phase and gain imbalances between in-phase (I) and quadrature (Q) components of a received signal base on a determination of peak amplitude” by Shahriar Emami, granted on Sep. 7, 1999, discloses a method for detecting an amplitude peak of demodulated I-phase and Q-phase components, and correcting the amplitude and phase imbalances between the I-phase and Q-phase components using the amplitude peak. In this patent, one of reference I/Q-phase components is established to be a reference phase, and another one is set to be an imbalance phase to find amplitude peaks of the respective phases and obtain the phase imbalances using a sine function. The patent by Shahriar Emami uses an arcsine function to obtain the phase imbalances between the I-phase and the Q-phase components, but when realizing the function through an actual digital circuit, the circuit becomes more complex, and its realization precision is reduced.
Therefore, when attempting to detect and compensate for the gain and phase imbalances between the I-phase and the Q-phase components, an improved method for solving the complexity of circuit realization and the noise sensitivity found in the above-noted patents is required.